nic_router: fix use of outdated ARP-cache entries

When a NIC session is destructed at the router, we have to remove all ARP
cache entries that match the MAC address of that session. Otherwise the
outdated entries might be re-applied later, leading to wrong destination
MAC addresses in routed packets.

Fixes #2637

repos/os/src/server/nic_router/arp_cache.cc

@@ -13,6 +13,8 @@
 
 /* local includes */
 #include <arp_cache.h>
+#include <domain.h>
+#include <configuration.h>
 
 using namespace Net;
 using namespace Genode;
@@ -48,6 +50,11 @@ Arp_cache_entry::find_by_ip(Ipv4_address const &ip) const
 	return entry->find_by_ip(ip);
 }
 
+void Arp_cache_entry::print(Output &output) const
+{
+	Genode::print(output, _ip, " > ", _mac);
+}
+
 
 /***************
  ** Arp_cache **
@@ -55,9 +62,15 @@ Arp_cache_entry::find_by_ip(Ipv4_address const &ip) const
 
 void Arp_cache::new_entry(Ipv4_address const &ip, Mac_address const &mac)
 {
-	if (_entries[_curr].constructed()) { remove(&(*_entries[_curr])); }
+	if (_entries[_curr].constructed()) {
+		remove(&(*_entries[_curr]));
+	}
 	_entries[_curr].construct(ip, mac);
-	insert(&(*_entries[_curr]));
+	Arp_cache_entry &entry = *_entries[_curr];
+	insert(&entry);
+	if (_domain.config().verbose()) {
+		log("[", _domain, "] new ARP entry ", entry);
+	}
 	if (_curr < NR_OF_ENTRIES - 1) {
 		_curr++;
 	} else {
@@ -73,3 +86,22 @@ Arp_cache_entry const &Arp_cache::find_by_ip(Ipv4_address const &ip) const
 
 	return first()->find_by_ip(ip);
 }
+
+
+void Arp_cache::destroy_entries_with_mac(Mac_address const &mac)
+{
+	for (unsigned curr = 0; curr < NR_OF_ENTRIES; curr++) {
+		try {
+			Arp_cache_entry &entry = *_entries[curr];
+			if (entry.mac() != mac) {
+				continue;
+			}
+			if (_domain.config().verbose()) {
+				log("[", _domain, "] destroy ARP entry ", entry);
+			}
+			remove(&entry);
+			_entries[curr].destruct();
+
+		} catch (Arp_cache_entry_slot::Deref_unconstructed_object) { }
+	}
+}

repos/os/src/server/nic_router/arp_cache.h

@@ -22,6 +22,7 @@
 
 namespace Net {
 
+	class Domain;
 	class Arp_cache;
 	class Arp_cache_entry;
 	using Arp_cache_entry_slot = Genode::Constructible<Arp_cache_entry>;
@@ -56,6 +57,14 @@ class Net::Arp_cache_entry : public Genode::Avl_node<Arp_cache_entry>
 		 ***************/
 
 		Mac_address const &mac() const { return _mac; }
+		Ipv4_address const &ip() const { return _ip; }
+
+
+		/*********
+		 ** log **
+		 *********/
+
+		void print(Genode::Output &output) const;
 };
 
 
@@ -68,6 +77,7 @@ class Net::Arp_cache : public Genode::Avl_tree<Arp_cache_entry>
 			NR_OF_ENTRIES = ENTRIES_SIZE / sizeof(Arp_cache_entry),
 		};
 
+		Domain const         &_domain;
 		Arp_cache_entry_slot  _entries[NR_OF_ENTRIES];
 		bool                  _init = true;
 		unsigned              _curr = 0;
@@ -76,8 +86,12 @@ class Net::Arp_cache : public Genode::Avl_tree<Arp_cache_entry>
 
 		struct No_match : Genode::Exception { };
 
+		Arp_cache(Domain const &domain) : _domain(domain) { }
+
 		void new_entry(Ipv4_address const &ip, Mac_address const &mac);
 
+		void destroy_entries_with_mac(Mac_address const &mac);
+
 		Arp_cache_entry const &find_by_ip(Ipv4_address const &ip) const;
 };
 

repos/os/src/server/nic_router/domain.h

@@ -98,7 +98,7 @@ class Net::Domain : public Domain_base
 		unsigned long                         _interface_cnt       { 0 };
 		Pointer<Dhcp_server>                  _dhcp_server         { };
 		Genode::Reconstructible<Ipv4_config>  _ip_config;
-		Arp_cache                             _arp_cache           { };
+		Arp_cache                             _arp_cache           { *this };
 		Arp_waiter_list                       _foreign_arp_waiters { };
 		Link_side_tree                        _tcp_links           { };
 		Link_side_tree                        _udp_links           { };

repos/os/src/server/nic_router/interface.cc

@@ -1022,6 +1022,8 @@ Interface::~Interface()
 		_dhcp_allocations.remove(allocation);
 		_destroy_dhcp_allocation(*allocation);
 	}
+	/* dissolve ARP cache entries with the MAC address of this interface */
+	_domain.arp_cache().destroy_entries_with_mac(_mac);
 }